The United Nations Security Council votes on a resolution that will require Syria to give up its chemical weapon, at UN Headquarters, Sept. 27, 2013. Saudi Arabia is rejected a seat on the UN Security Council and says the 15-member body is incapable of resolving world conflicts.

US-Saudi relations, a bedrock of the American relationship with the Middle East since World War II, forged on the back of oil wealth and defense partnerships, have been put under unprecedented public strain over the past week.

In the past week, Saudi Arabia rejected a seat on the United Nations Security Council (which it said was intended as a message to the US) and its intelligence chief announced he would be scaling back US-Saudi cooperation on war-torn Syria.

The US has launched an unprecedented push to reach an agreement with Saudi Arabia's chief rival, Iran, while Saudi Arabia has undermined US efforts to punish Egypt's military for a July coup by filling Egyptian coffers with promises of more money than the US has yanked back. The US abruptly retreated from a full march toward a military strike on Syria – a move Riyadh strongly backed.

Saudi officials have been quite blunt. Prince Turki al-Faisal, a member of the royal family and former director of Saudi intelligence, said in Washington that President Obama's Syria policy was "lamentable" and scoffed at the US-Russia agreement on Syria's chemical weapons deal, Reuters reports.

"The current charade of international control over Bashar's chemical arsenal would be funny if it were not so blatantly perfidious. And designed not only to give Mr. Obama an opportunity to back down (from military strikes), but also to help Assad to butcher his people," said Prince Turki.

For decades, Riyadh and Washington have been bound by a basic tradeoff: America guarantees protection from potential predators in the region, while Saudi Arabia supplies the lifeblood – relatively inexpensive oil – to run the world economy and pumps billions each year into the US arms industry. But America's failure to back Saudi Arabia on matters it considers vital to its security is raising questions in Riyadh about the value of that exchange.

"This is not how a protection racket is supposed to work," said Christopher Davidson, a scholar and author of After the Sheikhs: The Coming Collapse of the Gulf Monarchies. "Saudi Arabia is becoming increasingly dissatisfied with a relationship it thought it had in the bag, despite having handed over several percent of their GDP to Western arms companies." As a result, he said, "Saudi Arabia is retreating into its shell of countries that surround it and who rely on its aid and good will."

Saudi King Abdullah has urged the US to attack Iran, “cut off the head of the snake” and halt its nuclear program, U.S. diplomats reported in cables released by WikiLeaks in 2010. After last month’s accord on chemical weapons, Prince Saud said Assad’s government would probably use the deal as an opportunity “to impose more killing and to torture its people.”

“We don’t know what the Americans are trying to do with Syria,” said Khalid al-Dakhil, a political science professor at King Saud University in Riyadh. “They seem to be using Syria as a bargaining chip with Iran. They handed Iraq to the Iranians, and the Saudis won’t let them do the same thing to Syria.”

And on backing the Syrian rebels, an issue on which Washington and Riyadh were initially aligned, the divide is growing. An anonymous Saudi official told Bloomberg yesterday that Riyadh's support for Syrian rebels would not be "constrained" by US efforts to keep the money from Islamist groups.

The anonymous comments come on the heels of a London meeting between US Secretary of State John Kerry and his counterparts from countries backing the Syrian rebels. At the meeting, they agreed to send aid exclusively through the moderate Syrian National Coalition's armed wing to "curtail the influence of extremists."

"Syrian opposition factions backed by the US are disorganized and largely ineffective, so directing assistance only to them would be handicapping the fight against President Bashar al-Assad," the anonymous Saudi official said.

In the run-up to the expected U.S. strikes, Saudi leaders asked for detailed U.S. plans for posting Navy ships to guard the Saudi oil center, the Eastern Province, during any strike on Syria, an official familiar with that discussion said. The Saudis were surprised when the Americans told them U.S. ships wouldn't be able to fully protect the oil region, the official said.

Disappointed, the Saudis told the U.S. that they were open to alternatives to their long-standing defense partnership, emphasizing that they would look for good weapons at good prices, whatever the source, the official said.

In the second episode, one Western diplomat described Saudi Arabia as eager to be a military partner in what was to have been the U.S.-led military strikes on Syria. As part of that, the Saudis asked to be given the list of military targets for the proposed strikes. The Saudis indicated they never got the information, the diplomat said.

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"The Saudis are very upset. They don't know where the Americans want to go," said a senior European diplomat not in Riyadh.

Yet the anonymous Saudi official quoted by Bloomberg said that reports of a "major split are overblown," citing common interests in oil price stability and combating terrorism. Just last week, the US Department of Defense announced it would sell $10.8 billion in "advanced weaponry" to Saudi Arabia and ally United Arab Emirates.

A Western diplomat told the WSJ that Saudi Arabia's top priority is a more effective US or UN plan for helping the Syrian rebels.